The rubbers according to the present invention are understood to be synthetic rubbers used as elastomers, binders, or coating substances. The synthetic rubbers prepared by emulsion polymerization include, in particular, homopolymers of butadiene and chloroprene, as well as their copolymers with ethylenically-unsaturated compounds such as ethylenic and vinyl-aliphatic compounds; .alpha.-methylene carboxylic acids, their esters, nitriles and amides such as alkyl acrylates and methacrylates, acrylonitrile, acrylamide, methacrylonitrile, and methacrylamide; vinyl-aromatic compounds such as vinylnaphthalene; styrene; and substituted styrenes. Also included are polymers of 2,3-dichloro-1,3-butadiene. Modifiers can be incorporated in order to limit or fix the length of the polymer chain and its degree of crosslinking. They may contain fractions of the sol type (benzene- and toluene-soluble), the gel type, or solgel mixtures.
These rubbers are generally prepared by polymerization of the monomer or monomers in the aqueous phase in the presence of emulsifiers using surfactants such as primary and secondary alkyl sulfates or sulfonates, soaps of colophony of pine resin or of unprocessed or disproportionated, hydrogenated, or partially polymerized woods alone or in combination and with or without the presence of non-ionic surfactants such as condensates of ethylene oxide on fatty acids and fatty alcohols or on phenols. Known vulcanization systems can be incorporated partially or wholly into these rubbers. The resulting polymer is in the form of a fine stable disperson of rubber in the aqueous phase. Latexes and processes for preparing them are known. In general, latexes contain 10-60% by weight of solid material with respect to the total quantity of latex. The solid material can be recovered by coagulating the latex using, as coagulation agents, certain water-soluble salts with or without the presence of mineral or organic acids and with or without the presence of organic polyelectrolytes according to the nature of the emulsifier. Water-soluble salts known for coagulating properties include, in particular, the sulfates, chlorides, nitrates, and acetates of sodium, calcium, iron, zinc and aluminum.
However, coagulation in the presence of the usual water-soluble salts usually leads to formation of a coagulant or non-homogeneous lumps with particle sizes ranging from a few microns to one or more centimeters and in some cases having a strong tendency to reagglomerate, which, in the case of certain elastomers, can present difficulties in their separation from the aqueous phase and in their drying, storage, and subsequent handling. In the case of polychloroprene, this method is inapplicable and requires cold or hot coagulation processes.
In order to develop, the rubber industry thus needs to obtain and use free-running powders which are easy to store and handle, and usable in less sophisticated processing equipment than the conventional equipment.
The use of basic aluminum chloride for the preparation of powdered resins has been previously described in Japanese Patent Publication No. 14, 549/74, which applies it to resins containing 20-80% rubber polymers. According to this application, flocculation of the resin from the aqueous emulsion is carried out at ambient temperature followed by heating and then rapid cooling. This technique is not effective for obtaining powders from elastomer latexes.